This invention relates to the field of cranes and more particularly to control systems and methods for controlling residual pendulation associated with the movement of suspended payloads using rotary boom cranes.
One category of construction and transportation cranes consists of overhead gantry cranes. A second category of construction and transportation cranes consists of rotary cranes, of which there are two types: rotary jib cranes and rotary boom cranes.
Components of crane commands can induce sway of a payload. Sway control depends on the particular category of crane and its structural configuration.
Rotary Boom Cranes
A rotary boom crane configuration has a crane column horizontally rotatable about a vertical axis, a luffing boom attached to the column, and a pendulum-like hoist-line attached to the distal end of the boom. A rotary boom crane can have one translation degree of freedom (variable hoist-line length) and two rotation degrees of freedom: rotation about the crane column (slewing) and boom elevation through a vertical angle (luffing). Positioning of a payload that swings from the hoist-line is accomplished through luff, slew, and hoist commands. Because of differences in translational and rotational degrees of freedom between a rotary boom crane and a rotary jib crane, primarily due to the luffing boom, a rotary boom crane configuration has different payload dynamics and can require a different control system.
Cranes are used in virtually any large-scale construction or cargo transportation operation. In a typical construction or transportation crane maneuver, an operator uses translation, rotation, and lifting operations to move a container. Maneuvers are performed at rates sufficiently slow in order to reduce unwanted container pendulation. Unfortunately, slow crane maneuvers can increase the cost and time involved to move cargo. The operational approach to reduce payload residual pendulation is to reduce crane velocities and accelerations.
Overhead Gantry Cranes
Sway control has been disclosed for overhead gantry cranes. An overhead gantry crane incorporates a trolley which can translate in two directions in a horizontal plane. Attached to the trolley is a load-line for payload attachment, which can have varying load-line length.
Feddema et al., U.S. Pat. No. 5,785,191 (1998), is an example of operator control systems and methods for swing-free motion in gantry-style cranes. Feddema et al. discloses use of an infinite impulse response filter and a proportional-integral feedback controller to dampen payload sway in a crane having a trolley moveable in a horizontal plane and having a payload suspended by multiple variable-length cables for payload movement in a vertical plane.
Overhead gantry cranes are suitable for construction and transportation applications where the physical environment supports the crane""s required overhead structure. Overhead gantry cranes can have three translational degrees of freedom, two directions of trolley translation and one vertical translation of load-line length (for example, left-right, forward-backward, and up-down translations). Overhead gantry cranes have no rotation about an axis. Consequently, Feddema""s control system is limited to overhead gantry cranes and cannot work for cranes with different types of degrees of freedom, such as rotation about an axis as found in rotary cranes.
Rotary Jib Cranes
Sway control has been disclosed for rotary jib cranes. Rotary jib cranes have three degrees of freedom. The first is a rotation about a vertical axis at a crane base. The second is a horizontal translation of a trolley along a fixed-elevation jib, as in a gantry crane. The third is a variable load-line length, also a translation. When a payload is disturbed, the payload and load-line move like a spherical pendulum about the load-line to trolley attachment point. Robineff et al., U.S. Pat. No. 5,908,122 (1999), is an example of a sway control method and system for rotary jib cranes.
Oscillation control for a rotary jib crane configuration can account for one rotational axis (the jib) and two translational axes (trolley position along the jib and load-line length). See Parker et aL, xe2x80x9cOperator in-the-loop Control of Rotary Cranes,xe2x80x9d Proceedings of the SPIE Symposium on Smart Structures and Materials, Industrial Applications of Smart Structures Technologies, San Diego, Calif., Vol. 2721, pp. 364-372, Feb. 27-29, 1996, hereafter referred to as Parker""96. Parker""96 teaches an open-loop control method for reducing the oscillatory motion of rotary jib crane payloads during operator commanded maneuvers. The control method of Parker""96 works only for a rotary jib crane with three controllable motions: jib rotation in a horizontal plane about a vertical axis, trolley translation along a jib axis, and translational load-line length changes. The controllable motions result in two unactuated tangential and radial pendulation motions of the load-line and payload. Since the jib is fixed in a horizontal plane, payload elevation changes are only accomplished through changes in the load-line length. Consequently, Parker""96""s control system is limited to cranes with only one rotational axis (the jib) and two translational axes (trolley position along the jib and load-line length), and cannot work for cranes with different types of degrees of freedom as found in rotary boom cranes.
Payload Motion in a Rotarty Boom Crane
A payload moved by a rotary boom crane can have two oscillatory degrees of freedom. The first is payload pendulation tangential to an arc traced by the distal end of the boom while slewing the crane (or equivalently, a motion tangential to the column axis of rotation). The second is a payload pendulation radial to the column axis of rotation. Both radial and tangential pendulation have zero value when the hoist-line is parallel to a gravitational vector. At the end of a typical point-to-point maneuver, the payload will oscillate in these two directions. The degree of oscillation is dependent on the specific maneuver. Currently, an operator""s only option for mitigation of residual pendulation is to maneuver the payload slowly, contributing to higher construction and transportation costs.
Crane Control Systems
One class of crane control systems proposes to increase potential maneuver speed by controlling residual pendulation. One approach, command shaping, is an open loop approach for generating a maneuver which will not excite residual pendulation. A number of techniques for open-loop pendulation control crane operations have been developed. See, for example, Vaha et al., xe2x80x9cRobotization of an Offshore Container Crane,xe2x80x9d Robots: Coming of Age, Proceedings of the 19th ISIR International Symposium, pp. 637-648, 1988. However, Vaha""s approach does not compensate for radial pendulation, due to centripetal acceleration of a payload.
Sakawa and Nakazumi propose an open-loop plus closed-loop feedback control for automatic operation of a rotary crane which makes three kinds of motion (rotation, load hoisting, and boom hoisting) simultaneously. See Sakawa and Nakazumi, xe2x80x9cModeling and Control of a Rotary Crane,xe2x80x9d Journal of Dynamic Systems, Measurement, and Control, Vol. 107, pp. 200-206, 1985. Sakawa and Nakazumi propose control for automated rotary crane operation, but do not address rotary boom crane operation with an operator-in-the-loop.
A proposed rotary boom crane control system relies on modifications to a nominal crane system. See Ott, xe2x80x9cControl of Container cranes,xe2x80x9d Proceedings of the National Conference on Noise Control Engineering, Vol. 1, No. 1, pp. 407-410, 1996. Ott""s system could work for newly designed cranes, but Ott requires crane modification and does not work well with existing cranes.
Accordingly, there is an unmet need for reducing payload pendulation in rotary boom cranesxe2x80x94having luff, slew, and hoist velocitiesxe2x80x94with an operator-in-the-loop. Such cranes typically can be found in construction and ship-based applications.
This invention provides a new control system for filtering input commands to a rotary boom crane to reduce payload pendulation, using a command shaping filter to remove an identified payload pendulation frequency.
The present invention provides a new method for controlling rotary boom cranes. The present invention filters rotary boom crane operator input commands to reduce unwanted residual pendulation. The present invention implements command shaping filters, designed through the use of rotary boom crane kinematics and payload equations of motion. The present invention uses the filters to generate filtered signals to crane servo controllers, resulting in payload motion with minimal pendulation.
The present invention provides a command shaping control method for reducing payload pendulation caused by operator commanded maneuvers, in rotary boom cranes, such as those found in construction and cargo transportation.